Method for producing inorganic oxide particles

ABSTRACT

The present invention relates to a method for producing inorganic oxide particles, comprising at least the following steps of:
         coagulating a dispersion obtained by carrying out the hydrolysis reaction and the polycodensation reaction of a metal alkoxide in the presence of a basic catalyst;
           filtering the dispersion to obtain particles; and   drying the particles, wherein   the step of coagulating the dispersion is carried out by adding a coagulant comprising at least one compound selected from the group consisting of carbon dioxide, ammonium carbonate, ammonium hydrogen carbonate and ammonium carbamate to the dispersion.   
               

     The inorganic oxide particles obtained by the method of the present invention have high purity and are excellent in flowability.

TECHNICAL FIELD

The present invention relates to a method for producing inorganic oxideparticles. More specifically, it relates to a method for producinginorganic oxide particles, which makes extremely easy the filtration andcollection of inorganic oxide particles obtained by the hydrolysis andpolycondensation reaction (so-called “sol-gel method”) of a metalalkoxide in the presence of a basic catalyst.

BACKGROUND ART

The sol-gel method is known as one of the methods for producinginorganic oxide particles such as silica, titania, zirconia or aluminaparticles. This production method is to obtain inorganic oxide particlesby the hydrolysis reaction and polycondensation reaction of a metalalkoxide such as tetraethoxysilane in an organic solvent containingwater in the presence of an acidic catalyst or a basic catalyst. Thesol-gel method is characterized in that fine inorganic oxide particleswhich are spherical and relatively uniform in particle size areobtained.

In a dispersion of inorganic oxide particles obtained by the reaction ofthe sol-gel method, the inorganic oxide particles are highly dispersedas fine primary particles. Therefore, it is extremely difficult tocollect a cake (a concentrate of a dispersion containing inorganic oxideparticles in high concentration) of inorganic oxide particles from thisdispersion by filtration.

Then, to collect the cake from the above dispersion of inorganic oxideparticles, for example, a method in which a dispersion medium is removedby heating and/or depressurizing the dispersion or a method in which thedispersion is centrifuged to spin down the inorganic oxide particles andthen decantation is carried out is employed. The inorganic oxideparticles can be obtained by drying the cake obtained by the abovemethod to remove the dispersion medium remaining in the cake.

However, in the case of the above cake collection step, a firmlyagglomerated product of the inorganic oxide particles contained in thecake is formed, and further a firm agglomerate of the inorganic oxideparticles is formed by the subsequent drying step. Therefore, even whenthe inorganic oxide particles obtained by the above method aredisintegrated, fine inorganic oxide particles which are uniform inparticle size are not obtained. When the inorganic oxide particles arere-dispersed into a dispersion medium such as a resin or a solvent, theabove agglomerate is not easily disintegrated by the shear of adisperser and not uniformly dispersed in a dispersion medium. Especiallyin the case of fine inorganic oxide particles having a primary particlediameter of 1 μm or less produced by the reaction of the sol-gel method,the cohesion force of the particles is very strong and an extremely firmagglomerate is apt to be formed.

To solve the above problem, various proposals have been made up tillnow.

For example, JP-A 6-115925 proposes a method in which inorganic oxideparticles obtained by drying a dispersion of inorganic oxide particlesare disintegrated by a jet mill. According to this method, it ispossible to obtain inorganic oxide particles which are uniform inparticle size to some extent but the number of firm agglomerates formedat the time of drying cannot be reduced. Therefore, it cannot be saidthat this is not the technology for basically solving the above problem.

JP-A 2003-277025 discloses a method for preventing agglomeration byadding ethylene glycol to a dispersion of inorganic oxide particleswhile a dispersion medium is removed from the dispersion so as to solveproblems such as the agglomeration and sintering of a metal oxidewithout disintegration. According to this method, the formation of anagglomerate which is hardly disintegrated is suppressed but ethyleneglycol may remain in the inorganic oxide particles unless the drying andcalcination conditions are controlled precisely. Therefore, it isdifficult to adopt this method according to the application purpose ofthe inorganic oxide particles.

Printing is becoming faster and picture quality is becoming higher inelectrophotographic technologies for copiers and printers. Since thenumber of times of toner transfer increases in the copiers and printers,an additive for enhancing the transfer efficiency of a toner is becomingnecessary. It is reported that sol-gel silica (surface treated inorganicoxide particles) which has a narrow particle size distribution and ahydrophobilized surface is effective as the above additive (JP-A2002-108001).

To produce the sol-gel silica having a hydrophobized surface, there isproposed a method for obtaining hydrophobized silica by adding asilazane compound to silica sol to react it with the silica sol (JP-A2006-151764). The collection of a cake of silica after hydrophobizationin this method is carried out by distilling off a solvent from adispersion containing surface treated silica. Although this collectionmethod can be easily employed when silica is taken out from a flask in alaboratory scale, when this method is applied to an actual large-scaleproduction plant, it is difficult to scrape out a cake of thehydrophobic sol-gel silica from a reaction oven, which is not practical.Although it is conceivable that a filtration method is employed tocollect silica after hydrophobization, when the filtration method isemployed to collect fine particles having a particle diameter of 1 μm orless such as the particles produced by the sol-gel method, the particlespass through a filter paper or a filter cloth. When the solvent isremoved from the particles after filtration to dry the particles up, thehydrophobic sol-gel silica firmly agglomerate, whereby it may bedifficult to re-disperse it.

DISCLOSURE OF THE INVENTION

The present invention was made in view of the above situation. That is,it is an object of the present invention to provide a method for easilyproducing inorganic oxide particles synthesized by the sol-gel methodwhich have excellent flowability without agglomerating firmly. Theinorganic oxide particles may be surface treated inorganic oxideparticles whose surface is preferably hydrophobized.

The inventors of the present invention conducted intensive studies toattain the above object. As a result, they found that when a coagulantcomprising a specific compound is added to a dispersion of inorganicoxide particles obtained by the hydrolysis and polycondensation reactionof a metal alkoxide, that is, the sol-gel method in the presence of abasic catalyst, the inorganic oxide particles can be easily collected byfiltration which is a general solid-liquid separation method.

As described above, it was confirmed that the inorganic oxide particlesobtained by filtration after the addition of a specific coagulant do notagglomerate firmly and are excellent in disintegration properties ascompared with inorganic oxide particles taken out by a known solventdistillation-off method.

That is, the present invention is a method for producing inorganic oxideparticles, comprising at least the following steps of:

-   -   coagulating a dispersion obtained by carrying out the hydrolysis        reaction and the polycondensation reaction of a metal alkoxide        in the presence of a basic catalyst;    -   filtering the dispersion to obtain particles; and    -   drying the particles, wherein    -   the step of coagulating the dispersion is carried out by adding        a coagulant comprising at least one compound selected from the        group consisting of carbon dioxide, ammonium carbonate, ammonium        hydrogen carbonate and ammonium carbamate (to be simply referred        to as “coagulant” hereinafter) to the dispersion.

Surface treated inorganic oxide particles whose surface has beenhydrophobized can be produced by further carrying out at least one ofthe following two steps:

-   (1) a first surface treating step for carrying out a surface    treatment by adding at least one surface treating agent selected    from the group consisting of a silicone oil, a silane coupling agent    and a silazane to the dispersion before the step of coagulating the    dispersion; and-   (2) a second surface treating step for carrying out a surface    treatment by adding at least one surface treating agent selected    from the group consisting of a silicone oil, a silane coupling agent    and a silazane to the dried inorganic oxide particles after the    above drying step.

Both the above first surface treatment step and the second surfacetreatment step may be carried out.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described in detail hereinunder.

<<Method for Producing Inorganic Oxide Particles>> (1) Reaction ofSol-Gel Method

In the method of the present invention, first comes a reaction step forobtaining a dispersion of inorganic oxide particles dispersed in asolvent by the hydrolysis and polycondensation reaction of a metalalkoxide, that is, the reaction of the sol-gel method in the presence ofa basic catalyst.

The method for producing a dispersion containing inorganic oxideparticles by the sol-gel method is known, and this process can becarried out in the same manner as in the prior art even in the presentinvention. That is, a metal alkoxide which is a raw material ishydrolyzed and polycondensed in a suitable solvent in the presence of asuitable basic catalyst.

<Metal Alkoxide>

The metal alkoxide used in the production method of the presentinvention is not particularly limited if it is a compound used for theproduction of inorganic oxide particles by the reaction of the sol-gelmethod and is suitably selected according to the type of the inorganicoxide particles to be produced.

Examples of the metal alkoxide for obtaining the inorganic oxideparticles which will be described hereinafter in the present inventioninclude titanium alkoxides such as titanium tetraisopropoxide andtitanium tetra-n-butoxide; zirconium alkoxides such as zirconiumn-butoxide and zirconium t-butoxide; boron alkoxides such as trimethylborate and triethyl borate; aluminum alkoxides such as aluminumn-butoxide and aluminum isopropoxide; indium alkoxides such as indium(III) isopropoxide; silicon alkoxides (alkoxysilanes) such as methyltrimethoxysilane, methyl triethoxysilane, tetramethoxysilane,tetraethoxysilane, tetraisopropoxysilane and tetrabutoxysilane; andalkoxides of the group IV elements excluding silicon such as germanium(IV) isopropoxide, germanium (IV) methoxide and tin (IV) butoxide.

Out of the above metal alkoxides, titanium tetraisopropoxide, titaniumtetra-n-butoxide, zirconium n-butoxide, aluminum n-butoxide, aluminumisopropoxide, methyltrimethoxysilane, methyltriethoxysilane,tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane andtetrabutoxysilane are preferred, titanium tetraisopropoxide, zirconiumn-butoxide, tetramethoxysilane and tetraethoxysilane are more preferredas they can be easily acquired industrially and are easy to handle, andmethyltrimethoxysilane, tetramethoxysilane and tetraethoxysilane areparticularly preferred.

In the production method of the present invention, the above metalalkoxides may be used alone or in combination of two or more. When twoor more metal alkoxides are used in combination, composite inorganicoxide particles containing silica can be obtained by mixing analkoxysilane with a metal alkoxide excluding the alkoxysilane. Aftersilica particles having a certain diameter are obtained from thehydrolysis and polycondensation of an alkoxysilane, a metal alkoxideexcluding the alkoxysilane may be added to further carry out hydrolysisand polycondensation. In this case, composite inorganic oxide particlesin which another metal oxide is bonded to the surface of each silicacore particle can be obtained.

When the metal alkoxide is liquid at room temperature and atmosphericpressure, it may be used as it is or after it is diluted with an organicsolvent which will be described hereinafter. When the metal alkoxide issolid at room temperature and atmospheric pressure, it may be used afterit is dissolved or dispersed in an organic solvent.

<Basic Catalyst>

In the production of the inorganic oxide particles by the sol-gelmethod, a suitable catalyst is preferably used. In the sol-gel method,an acidic catalyst may be used. In the present invention, a basiccatalyst is used as it is easy to obtain spherical particles which areuniform in particle size. Although particle growth is often carried outafter pre-hydrolysis in the presence of an acidic catalyst in thesol-gel method, use of the acidic catalyst for the pre-hydrolysis is notexcluded and a basic catalyst should be used at the time of particlegrowth in the present invention.

As the basic catalyst used in the present invention, a known basiccatalyst which is used for the production of inorganic oxide particlesby the reaction of the sol-gel method may be preferably used.

Examples of the basic catalyst include an amine compound and an alkalimetal hydroxide. The amine compound is preferably used becausehigh-purity inorganic oxide particles which have a low total content ofimpurities containing a metal excluding the metal element constitutingthe inorganic oxide particles of interest are obtained. Examples of theamine compound include ammonia, methylamine, dimethylamine,trimethlamine, ethylamine, dimethylamine and trimethylamine. Out ofthese, ammonia is particularly preferably used as it is easily removeddue to its high volatility and the reaction rate of the sol-gel methodis high.

The above basic catalysts may be used alone or in combination of two ormore.

As the above basic catalyst, an industrially available basic catalystmay be used as it is (in a commercially offered state) or after it isdiluted with water or an organic solvent like ammonia water.Particularly preferably, the basic catalyst is diluted with water tocontrol its concentration as required so as to prepare an aqueoussolution as it can easily control the reaction rate. When an aqueoussolution of the basic catalyst is used, its concentration is preferably1 to 30 mass % as it is industrially easily acquired and itsconcentration is easily controlled.

The content of the basic catalyst may be suitably determined inconsideration of the reaction rates of the hydrolysis andpolycondensation reaction of the metal alkoxide. The basic catalyst isused to ensure that its content in the reaction solution becomespreferably 0.1 to 60 mass %, more preferably 0.5 to 40 mass % based onthe mass of the metal alkoxide in use.

<Solvent>

The solvent used in the hydrolysis and polycondensation reaction of theabove metal alkoxide in the present invention is preferably a polarsolvent. The polar solvent as used herein is an organic solvent whichdissolves 10 g or more of water per 100 g at room temperature andatmospheric pressure, or water. A plurality of organic solventsexcluding water may be used in combination. In this case, a mixture ofthe organic solvents should meet the above requirement.

Examples of the organic solvent which is a polar solvent excluding waterinclude alcohols such as methanol, ethanol, isopropyl alcohol andbutanol; ethers such as diethyl ether, tetrahydrofuran and dioxane; andamide compounds such as dimethyl formamide, dimethyl acetamide andN-methylpyrrolidone.

Since an alcohol is by-produced at the time of the reaction of thesol-gel method, it is particularly preferred to use an alcohol such asmethanol, ethanol, isopropyl alcohol or butanol out of these because itsuppresses the inclusion of unnecessary impurities into a dispersion ofthe inorganic oxide particles after the reaction and can be easilyremoved by heating.

The above organic solvents and water may be used alone or in combinationof two or more solvents.

The amount of the organic solvent or water may be suitably determinedaccording to the particle diameters of the inorganic oxide particles ofinterest and the desired concentration value of the inorganic oxideparticles in the inorganic oxide particle dispersion after the reactionof the sol-gel method. For example, when an alcohol is used as theorganic solvent, the amount of the alcohol based on the mass (100 mass%) of the inorganic oxide particle dispersion obtained by the reactionof the sol-gel method is preferably 10 to 90 mass %, more preferably 15to 80 mass %.

Water is indispensable for the reaction of the sol-gel method(therefore, the above polar solvent for dissolving water is used). Whenthe above basic catalyst is added as an aqueous solution and when wateris used as part or all of the solvent, water does not need to be addedto the reaction solution separately. However, in other cases, waterrequired for the sol-gel reaction must be added separately.

The amount of water is suitably adjusted and selected according to theparticle diameters of the inorganic oxide particles to be produced. Whenthe amount of water is too small, the reaction rate becomes slow andwhen the amount is too large, drying (removal of the solvent) takeslong. Therefore, the amount of water is selected in consideration ofthese. The amount of water is preferably 2 to 50 mass %, more preferably5 to 40 mass % based on the total mass of the inorganic oxide particledispersion obtained by the reaction of the sol-gel method.

Water may be used as part or all of the reaction solvent and may beadded to the reaction solution after all reaction raw materialsexcluding water are prepared. However, to promote the reaction of thesol-gel method swiftly and stably, it is preferred that water should beused as part of the solvent, that is, a mixture of water and an organicsolvent should be used as the solvent. As for water as a solvent as usedherein, a case where water is added by the addition of a basic catalystis also included.

<Reaction Conditions>

The hydrolysis and polycondensation reaction (reaction of the sol-gelmethod) in the present invention are carried out in the presence of abasic catalyst as described above. Known conditions may be adopted asthe reaction conditions, and the method of contacting the metal alkoxideto the basic catalyst is not particularly limited and may be suitablyselected and determined in consideration of the constitution of areactor and a reaction scale.

One example of the reaction method in the sol-gel method is given below.

Water, a polar solvent (organic solvent) excluding water and a basiccatalyst are placed into a vessel, and a metal alkoxide (or an organicsolvent solution of a metal alkoxide) and an aqueous solution of a basiccatalyst are added to the reactor at the same time. According to thismethod, the vessel efficiency is high and spherical inorganic oxideparticles which are uniform in particle size can be manufacturedefficiently at high producibility advantageously. In this case, afterpart of the metal alkoxide is added, the remaining metal alkoxide andthe basic catalyst may be added at the same time.

When two or more metal alkoxides are used in combination, they may bemixed together and added simultaneously, or they may be addedsequentially. Particularly when a composite inorganic oxide containingsilica is to be produced, the pre-hydrolysis and polycondensationreaction of one of the metal alkoxides are first carried out and thenthe other metal alkoxide is added to continue the reaction, therebymaking it possible to produce composite metal oxide particles. Forexample, the hydrolysis and polycondensation reaction of an alkoxysilanein methanol in the presence of hydrochloric acid are carried out tohydrolyze the alkoxysilane with the acidic catalyst and then a metalalkoxide excluding the alkoxysilane, such as titanium tetraisopropoxide,is added to continue the reaction, thereby making it possible to producea composite inorganic oxide having a core made of silica and a shellmade of titania.

As for the addition of the metal alkoxide and the basic catalyst, theyare preferably added directly into the reaction liquid a little at atime. The expression “added directly into the reaction liquid a littleat a time” means that the end of a drip tube opening is immersed in thereaction liquid when the above raw material is added dropwise to thereaction liquid. The position of the end of the drip tube opening is notparticularly limited if it is in the liquid but desirably a positionnear an agitating blade where stirring is fully carried out anddroppings can be diffused into the reaction liquid swiftly.

The addition time of the metal alkoxide and the basic catalyst (a periodof time from the start of addition to the end of addition) is a veryimportant factor in the production of particles having a narrow particlesize distribution. When this addition time is too short, the particlesize distribution tends to become wide and when the addition time is toolong, stable particle growth becomes impossible. Therefore, to obtaininorganic oxide particles having a narrow particle size distribution anduniform in particle size, an addition time suitable for particle growthmust be adopted. From this point of view, the above addition time ispreferably 0.2 to 8 hours per 100 nm of the desired particle diameter.

The reaction temperature is not particularly limited if it is atemperature at which the reaction of the sol-gel method proceeds swiftlyand suitably selected according to the particle diameters of theinorganic oxide particles of interest. In general, as the reactiontemperature becomes lower, the particle diameters of the obtainedinorganic oxide particles become larger. To obtain inorganic oxideparticles having a median diameter of 0.01 to 5 μm, the reactiontemperature is suitably selected from a range of −10 to 60° C.

To enable the reaction of the sol-gel method to proceed without fail,after the addition of the metal alkoxide and the basic catalyst, ageing(existence of a time interval before the addition of a surface treatingagent) may be carried out. In this case, the ageing temperature ispreferably the same as the reaction temperature, that is, −10 to 60° C.,and the ageing time is preferably 0.25 to 5 hours.

To obtain inorganic oxide particles having a desired particle diameter,a metal alkoxide and a basic catalyst may be added again after ageing toincrease the particle diameters of the inorganic oxide particles.

<Dispersion of Inorganic Oxide Particles>

The dispersion obtained by the above method contains inorganic oxideparticles corresponding to the element of the above metal alkoxide usedas the raw material. What kind of inorganic oxide particles are obtainedaccording to the type, amount and addition order of the metal alkoxidein use would be obvious for people having ordinary skill in the art.

Out of the inorganic oxides, silicon, titanium, zirconium or aluminumoxide and composite inorganic oxides containing two or more of theseelements are preferred. Silica or a composite inorganic oxide containingsilicon and another metal element is more preferred and silica is mostpreferred because it has high reactivity with a surface treating agentwhich will be described hereinafter and excellent physical propertieswhen it is used as an external additive for toners.

Although the median diameter of the inorganic oxide particles obtainedby the reaction of the sol-gel method is generally 0.01 to 5 μm, theproduction method of the present invention can be employed regardless ofthe particle diameters of the inorganic oxide particles. It is difficultto collect inorganic oxide particles having a median diameter of 1 μm orless by filtration which is generally employed by solid-liquidseparation. When the method of the present invention is employed for theproduction of inorganic oxide particles having a median diameter of 0.01to 1 μm, inorganic oxide particles having a small particle diameter canbe easily collected advantageously.

The inorganic oxide particles produced by the reaction of the sol-gelmethod are characterized by a narrow particle size distribution. Theinorganic oxide particles obtained by the above production method have avery narrow particle size distribution. For example, the variationcoefficient as one of the indices of the width of a particle sizedistribution of can be set to 40% or less. In the present invention, thevariation coefficient can also be set to 30% or less. However, theproduction method of the present invention can be employed regardless ofthe particle size distribution width of the inorganic oxide particlescontained in the dispersion.

The inorganic oxide particles contained in the dispersion obtained bythe above method are dispersed in a mixed solvent of the polar solventin use and an alcohol produced by the hydrolysis of the metal alkoxide.

When the content of the inorganic oxide particles in the dispersion istoo high, the viscosity of the dispersion becomes too high, therebymaking it difficult to handle it. When the content of the inorganicoxide particles in the dispersion is too low, the amount of theinorganic oxide particles obtained by one time of the reaction becomessmall, which is uneconomical. From this point of view, the content ofthe inorganic oxide particles in the obtained inorganic oxide particledispersion is preferably 1 to 40 mass %, particularly preferably 2 to 25mass %. Therefore, the amount of the polar solvent, especially the polarsolvent excluding water is preferably adjusted to ensure that thecontent of the inorganic oxide particles falls within the above range.When the content of the inorganic oxide particles in the dispersionobtained by the reaction of the sol-gel method is too high and thereforeit is difficult to handle the dispersion, it is preferred to carry outthe control of the content of the inorganic oxide particles by addingthe polar solvent before the surface treating step which will bedescribed next.

(2) First Surface Treating Step

In the method for producing inorganic oxide particles, comprising thesteps of coagulating the dispersion obtained as described above,filtering it to obtain particles and drying the particles, the step ofcoagulating the dispersion is carried out by adding a coagulantcomprising at least one compound selected from the group consisting ofcarbon dioxide, ammonium carbonate, ammonium hydrogen carbonate andammonium carbamate to the dispersion.

However, in the method of the present invention, before the step ofcoagulating the above dispersion, a surface treatment (first surfacetreatment) may be carried out by adding at least one surface treatingagent selected from the group consisting of a silicone oil, a silanecoupling agent and a silazane to the dispersion.

As the above silicone oil, known silicone oils which are generally usedfor the surface treatment of inorganic oxide particles may be usedwithout restriction, and a suitable silicone oil is selected and usedaccording to the required performance of surface treated inorganic oxideparticles.

Examples of the silicone oil include dimethyl silicone oil, methylphenyl silicone oil, methyl hydrogen silicone oil, alkyl modifiedsilicone oil, amino modified silicone oil, epoxy modified silicone oil,carboxyl modified silicone oil, carbinol modified silicone oil,methacryl modified silicone oil, polyether modified silicone oil andfluorine modified silicone oil.

By using dimethyl silicone oil out of these, the hydrophobilization ofthe inorganic oxide particles can be carried out efficiently.

The amount of the silicone oil is not particularly limited but when itis too small, the surface treatment becomes unsatisfactory and when itis too large, a post-treatment becomes complicated. Therefore, theamount of the silicone oil is preferably 0.05 to 80 parts by mass, morepreferably 0.1 to 60 parts by mass based on 100 parts by mass of theinorganic oxide particles in use.

As the above silane coupling agent, known silane coupling agents whichare generally used for surface treatment may be used withoutrestriction, and a suitable silane coupling agent is selected and usedaccording to the required performance of surface treated inorganic oxideparticles.

Examples of the silane coupling agent include methyl trimethoxysilane,methyltriethoxysilane, hexyltrimethoxysilane, decyltrimethoxysilane,phenyltriethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane,(3-methacryloyloxypropyl)trimethoxysilane,(3-methacryloyloxypropyl)triethoxysilane,(3-acryloyloxy)-trimethoxysilane, (3-glycidoxypropyl)trimethoxysilane,(3-glycidoxypropyl)triethoxysilane, (3-aminopropyl)-trimethoxysilane,(3-aminopropyl)triethoxysilane,[N-(2-aminoethyl)-3-aminopropyl]trimethoxysilane,[N-(2-aminoethyl)-3-aminopropylmethyl]dimethoxysilane,(N-phenyl-3-aminopropyl)trimethoxysilane,(N,N-dimethyl-3-aminopropyl)trimethoxysilane,(N,N-diethyl-3-aminopropyl)trimethoxysilane and4-styryltrimethoxysilane.

Out of these, methyltrimethoxysilane, methyltriethoxysilane,hexyltrimethoxysilane and decyl trimethoxysilane are preferred becausethe hydrophobization of the inorganic oxide particles can be carried outefficiently.

The amount of the silane coupling agent is not particularly limited butwhen it is too small, the surface treatment becomes unsatisfactory andwhen it is too large, the post-treatment becomes complicated. Therefore,the amount of the silane coupling agent is preferably 0.05 to 80 partsby mass, more preferably 0.1 to 40 parts by mass based on 100 parts bymass of the inorganic oxide particles in use.

As the above silazane, known silazanes which are generally used forsurface treatment may be used without restriction. Out of the silazanes,hexamethylsilazane is preferred because it is highly reactive and easyto handle.

The amount of the silazane is not particularly limited but when it istoo small, the surface treatment becomes unsatisfactory and when it istoo large, the post-treatment becomes complicated. Therefore, the amountof the silazane is preferably 0.1 to 150 parts by mass, more preferably1 to 120 parts by mass based on 100 parts by mass of the inorganic oxideparticles in use.

The above surface treating agents may be used alone or in combination oftwo or more.

Out of the above surface treating agents, at least one selected from thegroup consisting of a silane coupling agent and a silazane is preferablyused, and a silazane is more preferably used as the flowability of theobtained surface treated inorganic oxide particles becomes high.

The method of adding the surface treating agent is not particularlylimited. When the surface treating agent is a low-viscosity liquid atroom temperature and atmospheric pressure, it may be added dropwise tothe dispersion or sprayed upon the dispersion. Preferably, it is addeddropwise to the dispersion because the operation is easy. When thesurface treating agent is a high-viscosity liquid or solid, it is addedto a suitable organic solvent to prepare a solution or a dispersionwhich is then added in the same manner as the low-viscosity liquid. Theorganic solvent used herein is the same as the above polar solvent.Further, when the surface treating agent is gaseous, it is blown intothe dispersion to become fine bubbles.

The treating temperature for the first surface treatment may bedetermined in consideration of the reactivity of the surface treatingagent in use. However, when the treating temperature is too low, theproceeding of the reaction becomes slow and when the treatingtemperature is too high, the operation becomes troublesome. Therefore,the treating temperature is preferably 10 to 100° C., more preferably 20to 80° C.

The treating time for the first surface treatment is not particularlylimited and may be determined in consideration of the reactivity of thesurface treating agent in use. In consideration of the completeproceeding of the surface treating reaction and the reduction of theprocess time, the treating time is preferably 0.1 to 48 hours, morepreferably 0.5 to 24 hours.

(3) Coagulation Step

In the method of the present invention, the coagulation of thedispersion obtained as described above is carried out without the abovefirst surface treatment (2) or after the first surface treatment (2).

This coagulation step is carried out by adding a coagulant comprising atleast one compound selected from the group consisting of carbon dioxide,ammonium carbonate, ammonium hydrogen carbonate and ammonium carbamateto the dispersion. By adding the above coagulant to the dispersion, aweak agglomerate of the inorganic oxide particles is formed in thedispersion. This agglomerate can be existent stably in the dispersiondue to the existence of the coagulant or a derivative thereof in thedispersion and therefore can be easily collected by filtration.

A technology for forming an agglomerate of inorganic oxide particles byadding a metal salt to a dispersion of the inorganic oxide particles isknown. According to this method, when a sodium salt or a potassium saltis used, it is possible that a metal element component constituting thesalt is contained in the obtained inorganic oxide particles, therebyrequiring a cleaning (purification) operation for removing this, whichis industrially disadvantageous.

In contrast to this, as the above coagulant used in the presentinvention is easily decomposed and removed by slight heating,high-purity inorganic oxide particles can be easily produced. Accordingto the method of the present invention, the content of elemental sodiumin the obtained inorganic oxide particles can be reduced to 100 ppm orless, preferably 10 ppm or less.

The amount and the addition method of the coagulant may be set asfollows according to the type of the coagulant in use. The amount of thecoagulant is set in consideration of balance between the degree offorming a weak agglomerate of inorganic oxide particles in thedispersion and the pointlessness of using an unduly large amount of theraw material. The mass of the inorganic oxide particles which is thebasis of the amount of the coagulant below is a value based on thesupposition that all the metal alkoxide in use is hydrolyzed andpolycondensed to become inorganic oxide particles.

In the case of any coagulant, the preferred amount of the coagulant whenboth the above first surface treatment and the second surface treatmentwhich will be described hereinafter are not carried out differs from theamount of the coagulant when at least one of the surface treatments iscarried out.

When carbon dioxide is used as the above coagulant, the amount thereofis preferably 0.005 part or more by mass, more preferably 0.005 to 300parts by mass based on 100 parts by mass of the inorganic oxideparticles contained in the dispersion. When no surface treatment iscarried out on the inorganic oxide particles, the amount of carbondioxide is preferably 0.05 part or more by mass, more preferably 0.05 to300 parts by weight, particularly preferably 0.25 to 200 parts by massbased on 100 parts by mass of the inorganic oxide particles. When thesurface treatment is carried out on the inorganic oxide particles, theamount of carbon dioxide is preferably 15 parts or more by mass, morepreferably 15 to 300 parts by mass, particularly preferably 17 to 200parts by mass based on 100 parts by mass of the inorganic oxideparticles.

Examples of the method of adding carbon dioxide include one in whichcarbon dioxide in a gaseous state is blown into the dispersion and onein which carbon dioxide in a solid state (dry ice) is added. Out ofthese, the latter method in which carbon dioxide in a solid state isadded is preferred as the operation is simple.

When ammonium carbonate, ammonium hydrogen carbonate or ammoniumcarbamate is used as the above coagulant, the amount thereof ispreferably 0.001 part or more by mass, more preferably 0.001 to 80 partsby mass based on 100 parts by mass of the inorganic oxide particlescontained in the dispersion. When no surface treatment is carried out onthe inorganic oxide particles, the amount of ammonium carbonate,ammonium hydrogen carbonate or ammonium carbamate is preferably is 0.001to 15 parts by mass, particularly preferably 0.001 to 10 parts by massbased on 100 parts by mass of the inorganic oxide particles. When thesurface treatment is carried out on the inorganic oxide particles, theamount of ammonium carbonate, ammonium hydrogen carbonate or ammoniumcarbamate is preferably 15 parts or more by mass, more preferably 15 to80 parts by mass, much more preferably 17 to 60 parts by mass,particularly preferably 20 to 50 parts by mass based on 100 parts bymass of the inorganic oxide particles.

Ammonium carbonate, ammonium hydrogen carbonate or ammonium carbamatemay be added in a solid state or dissolved in a suitable solvent to beadded as a solution. The solvent which is used to add the abovecoagulant as a solution is not particularly limited if it dissolve thecoagulant. However, water is preferably used as it has high dissolutionability and is easily removed after filtration. The concentration of asolution of ammonium carbonate, ammonium hydrogen carbonate or ammoniumcarbamate is not particularly limited if the coagulant is dissolved.However, when the concentration is too low, the amount of the solutionbecomes large, which is uneconomical. Therefore, the concentration ispreferably 2 to 15 mass %, particularly preferably 5 to 12 mass %.

The above coagulants may be used alone or in combination of two or more.

A mixture of ammonium hydrogen carbonate and ammonium carbamate, whichis marketed as so-called “ammonium carbonate”, may be used as it is orafter it is dissolved in a suitable solvent. The total amount ofammonium hydrogen carbonate and ammonium carbamate, the type of thesolvent used to add these as a solution and the concentration of thesolution are the same as those in the case of ammonium carbonate,ammonium hydrogen carbonate or ammonium carbamate.

The coagulant in the present invention is preferably at least oneselected from the group consisting of ammonium hydrogen carbonate andammonium carbamate, more preferably ammonium hydrogen carbonate,particularly preferably an aqueous solution of ammonium hydrogencarbonate.

pH of the inorganic oxide particle dispersion when the coagulant isadded is desirably selected from a range which ensures that thecoagulant does not cause unpreferred decomposition in the dispersion andthe effect of the present invention can be obtained effectively. Fromthis point of view, pH of the dispersion is set to preferably analkaline range, more preferably 9 or more.

The temperature of the inorganic oxide particle dispersion when thecoagulant is added is desirably set to ensure that a weak agglomerate ofthe inorganic oxide particles formed by the addition of the coagulantcan be existent stably. From this point of view, the temperature of thedispersion is preferably −10 to 60° C. which is the same as the reactiontemperature of the sol-gel method, more preferably 10 to 40° C.

After the addition of the coagulant, it is preferred that ageing shouldbe carried out, that is, a time interval should exist before thesubsequent filtration step. By carrying out ageing after the addition ofthe coagulant, the formation of the above weak agglomerate of theinorganic oxide particles is promoted advantageously. Although a longerageing time is better, a too long ageing time is uneconomical. When theageing time is too short, the formation of a weak agglomerate of theinorganic oxide particles becomes unsatisfactory. The ageing time ispreferably 0.5 to 72 hours, particularly preferably 1 to 48 hours. Thetemperature of the dispersion at the time of ageing is not particularlylimited and may be within the same temperature range as that for addingthe coagulant. The same temperature as that for adding the coagulantsuffices.

(4) Filtration Step

In the method of the present invention, next comes the step ofcollecting the inorganic oxide particles by filtration from thedispersion obtained by adding the coagulant preferably after ageing iscarried out as described above.

The inorganic oxide particles which form a weak agglomerate by addingthe above coagulant can be easily collected by filtration. Thefiltration method is not particularly limited and a known method such asvacuum filtration, pressure filtration or centrifugal filtration may beemployed.

A filter paper, a filter or a filter cloth (to be generically referredto as “filter paper or the like” hereinafter) used for filtration may beused without restriction if they can be industrially acquired andsuitably selected according to the scale of a separation apparatus(filtering mechanism). According to the present invention, since a weakagglomerate of primary particles is formed by adding the coagulant, theopening size of the filter paper or the like should be much larger thanthe primary particle diameter. For example, when the inorganic oxideparticles have a median diameter of 0.01 to 5 μm, a filter paper or thelike having an opening size of about 5 μm suffices. Since a filter paperor the like having a large opening size can be used, the inorganic oxideparticles can be filtered quickly.

The inorganic oxide particles are collected as a cake by filtration.

When an aqueous solution of ammonium hydrogen carbonate is used as thecoagulant in the above coagulating step (3), the solvent, the basiccatalyst and the unreacted surface treating agent used in the reactionof the sol-gel method can be decomposed or removed by rinsing theobtained cake with a suitable solvent such as water or an alcohol.

(5) Drying Step

Then, the inorganic oxide particles collected by the above filteringstep (4) are dried in this step.

In the present invention, when the cake of the inorganic oxide particlescollected as described above is dried at a temperature of 35° C. orhigher, its disintegration properties are further improved. Therefore,the drying temperature in the drying step of the present invention ispreferably 35° C. or higher. By heating at this temperature, thecoagulant remaining in the cake without being removed by the abovefiltration and rinsing can be easily removed by thermal decomposition.This is also one of the big advantages of the present invention.

The drying method is not particularly limited and a known method such asair drying or drying under reduced pressure may be employed. However,since it was made clear by studies conducted by the inventors of thepresent invention that the inorganic oxide particles are more easilydisintegrated when they are dried under reduced pressure than when theyare dried under atmospheric pressure, it is preferred to employ dryingunder reduced pressure.

A higher drying temperature is more advantageous from the viewpoint ofthe decomposition efficiency of the coagulant and the acquisition ofinorganic oxide particles which are easily disintegrated. However, whenthe drying temperature is too high, the substituent introduced into thesurfaces of the inorganic oxide particles by the surface treatment isdecomposed disadvantageously. Further, when the drying temperature istoo high, the content of water on the surfaces of the inorganic oxideparticles becomes too low, wherein when the obtained inorganic oxideparticles are used as an external additive for toners, the rate ofcharge rise drops disadvantageously. Therefore, to balance between them,the drying temperature is preferably 35 to 200° C., more preferably 50to 200° C., much more preferably 80 to 200° C., particularly preferably120 to 200° C.

Although the drying time is not particularly limited, when it is 2 to 48hours, the inorganic oxide particles can be completely dried.

(6) Second Surface Treating Step

In the method of the present invention, a surface treatment (secondsurface treatment) may be carried out by further adding at least onesurface treating agent selected from the group consisting of a siliconeoil, a silane coupling agent and a silazane to the inorganic oxideparticles obtained as described above.

The surface treating agent which can be used in this step may be thesame as those explained as the surface treating agent for carrying outthe above first surface treatment. However, in this second surfacetreating step, it is preferred to use a surface treating agent which canbe chemically bonded to a functional group on the surfaces of theinorganic oxide particles directly since the obtained surface treatedoxide particles have excellent flowability as compared with a case wherea surface treating agent having no reactivity (for example, an ordinarysilicone oil) is used.

The amount of the surface treating agent in the second surface treatmentstep is as follows according to its type.

Silicone oil: preferably 0.01 to 50 parts by mass, more preferably 0.01to 20 parts by mass based on 100 parts by mass of the inorganic oxideparticles after the first surface treatment;Silane coupling agent: preferably 0.01 to 100 parts by mass, morepreferably 0.2 to 50 parts by mass based on 100 parts by mass of theinorganic oxide particles after the first surface treatment; andSilazane: preferably 0.10 to 150 parts by mass, more preferably 0.2 to100 parts by mass based on 100 parts by mass of the inorganic oxideparticles after the first surface treatment.

The second surface treatment in this step is preferably carried out in aso-called “dry process”. That is, the above surface treating agent isadded to the inorganic oxide particles obtained through the drying stepand stirred by a suitable method. The method of adding the surfacetreating agent to the oxide particles may be suitably determinedaccording to the form of the surface treating agent in use. For example,when the surface treating agent is a low-viscosity liquid at a processtemperature and a process pressure, it may be added dropwise to theinorganic oxide particles or sprayed upon the inorganic oxide particles.When the surface treating agent is a high-viscosity liquid or solid, itmay be added in the same manner as the low-viscosity liquid after it isdiluted with a small amount of a suitable organic solvent. Examples ofthe organic solvent used herein are the same as the polar solventsexplained in (1) Reaction of the sol-gel method. Further, when thesurface treating agent is gaseous, the inorganic oxide particles and thesurface treating agent are stirred while they are kept airtight in avessel.

The second surface treatment in this step is preferably carried out inthe presence of water in order to keep a sufficient amount of a silanolgroup which can react with the surface treating agent on the surfaces ofthe inorganic oxide particles. In this case, the amount of water ispreferably 30 parts or less by mass, more preferably 0.2 to 20 parts bymass based on 100 parts by mass of the inorganic oxide particle.

The preferred treating conditions when the second surface treating stepis carried out are as follows.

Treating temperature: preferably 100 to 500° C., more preferably 150 to350° C.;Treating pressure: preferably 3×10⁵ or less, more preferably 1×10⁴ to2×10⁵ Pa; andTreating time: preferably 1 to 300 minutes, more preferably 5 to 180minutes.

The second surface treatment in this step may be carried out once or twoor more times. When the second surface treatment is carried out two ormore times, the types and amounts of the surface treating agents in useand treating conditions may be the same or different each time.Particularly when a different surface treating agent is used each time,surface treated oxide particles having finely controlled surfaceproperties can be obtained.

<<Inorganic Oxide Particles>>

The inorganic oxide particles of the present invention produced asdescribed above have excellent flowability. The surface treatedinorganic oxide particles obtained by the method of the presentinvention have a very low total content of impurities such as nitrogen.To further improve the flowability of the inorganic oxide particles ofthe present invention, it is preferred that at least one of the firstsurface treatment step (2) and the second surface treatment step (6)should be carried out, and it is more preferred that both of them shouldbe carried out.

The flowability of the surface treated inorganic oxide particles can beevaluated as agglomeration degree and as this value becomes smaller, theflowability becomes higher.

This agglomeration degree can be calculated as follows. After a sievehaving an opening of 355 μm, a sieve having an opening of 250 μm and asieve having an opening of 150 μm (all of them are sieves having adiameter of 75 mm based on JIS Z8801) are placed one upon another inthis order from the top at fixed intervals (2 cm), 5 g of the particlesis put on the top sieve, and these sieves are vibrated vertically at anamplitude of 1 mm and a frequency of 60 Hz for 15 seconds, the amountsof the remaining particles on these sieves are measured and insertedinto the following equation.

Agglomeration degree (%)={(amount of remaining particles on topsieve+amount of remaining particles on middle sieve×0.6+amount ofremaining particles on bottom sieve×0.2}÷initial mass of surface treatedinorganic oxide particles×100

This agglomeration degree can be easily measured by using a commerciallyavailable particulate characteristic measuring instrument, for example,the Powder Tester (registered trademark) of Hosokawa Micron Corporation.

When the inorganic oxide particles obtained by the method of the presentinvention are subjected to at least one of the first surface treatmentand the second surface treatment, the agglomeration degree thereof canbe set to 60% or less or further to 50% or less.

The nitrogen content of the inorganic oxide particles can be determinedby a method in which the oxide particles are completely oxidized at ahigh temperature and elemental analysis is made on the particles.

The nitrogen content of the inorganic oxide particles obtained by themethod of the present invention can be set to 0.05% or less or furtherto 0.02% or less.

Since the surface treated inorganic oxide particles obtained by themethod of the present invention have excellent flowability as describedabove, preferably, the surface thereof is highly hydrophobized, they canbe advantageously used as an external additive for toners or an externaladditive for coating materials.

When the surface treated inorganic oxide particles obtained by themethod of the present invention are used as an external additive fortoners, as the surface treated inorganic oxide particles have excellentflowability, they can increase the surface overage of resin particlesfor toners. Since the surface treated inorganic oxide particles obtainedby the preferred method of the present invention are highlyhydrophobized and the adsorption and dissociation of water on thesurface which causes the leakage of toner charge hardly occur, chargestability is high. Since water is existent on the surfaces of theparticles, the rate of charge rise becomes high advantageously. Sinceinorganic oxide particles produced by the conventional sol-gel methodcontain a significant amount of water capable of adsorption anddissociation, when they are used as an external additive for toners, theleakage of toner charge readily occurs, whereby charge stabilitydegrades.

Since the surface treated inorganic oxide particles obtained by themethod of the present invention have hydrophobic nature, they can beadvantageously used as an additive for resin materials such as epoxyresin and acrylic resin.

Further, since the inorganic oxide particles obtained by the method ofthe present invention have extremely high purity, when they are used asa sealant for semiconductors or an external additive for toners, theycan be advantageously used without contaminating a material of interest.

EXAMPLES

The following examples and comparative examples are provided for thepurpose of further illustrating the present invention but are in no wayto be taken as limiting. The methods of measuring physical properties inthe present invention are as follows.

(1) Measurement of Median Diameter of Inorganic Oxide ParticlesContained in Dispersion

The median diameter of the inorganic oxide particles contained in thedispersion was measured by an image analyzing method using a scanningelectron microscope (to be referred to as “SEM” hereinafter).

The dispersion of the inorganic oxide particles obtained after the endof the sol-gel reaction was diluted with pure water and the diluteddispersion was dropped on a silicon wafer. Thereafter, it was driedunder reduced pressure at room temperature for 2 or more hours to removethe dispersion medium, and the obtained product was used as a sample forSEM observation. The median diameter of the formed sample was obtainedby observing the formed sample through SEM several times by changing theimaging site and converting the calculated value as the particlediameter D₅₀ of 200 or more inorganic oxide particles into avolume-based value.

(2) Measurement of Median Diameter and Variation Coefficient ofInorganic Oxide Particles

The median diameter of the inorganic oxide particles finally obtained ineach example was measured by the following laser diffraction scatteringmethod.

The inorganic oxide particles obtained in each example were pounded in amortar, 0.1 g of the pounded particles was collected and placed into aglass bottle having an inner diameter of 4 cm and a height of 11 cm, and50 g of pure water was placed into the glass bottle in Examples 1-1 to1-11, Comparative Examples 1-1 and 2-1 and Reference Examples 1-2, 1-2and 2-1 whereas 50 g of ethanol was placed into the glass bottle inExamples 2-1 to 2-19. A part 4.5 cm from the end of a probe (the innerdiameter of the end: 7 mm) was immersed in this, and ultraviolet waveswere applied at an output of 50 W and 40 kHz for 30 minutes to dispersethe particles.

The median diameter and the variation coefficient of the obtaineddispersion were measured by polarization scattering intensity differencemetering using the Coulter LS230 (trade name) of Beckman Coulter Inc. ata range of 0.04 to 2000 μm. The variation coefficient was calculatedfrom the following equation.

Variation coefficient (%)=standard deviation of particle diameters(μm)/number average value of particle diameters (μm)

As the variation coefficient become smaller, the particle sizedistribution becomes narrower.

(3) Measurement of Crush Strength

The inorganic oxide particles obtained in each example were put througha sieve having an opening of 1.4 mm and then through a sieve having anopening of 0.71 mm to measure inorganic oxide particles remaining on thesieve having an opening of 0.71 mm.

The inorganic oxide particles remaining on the sieve having an openingof 0.71 mm were put on an even balance, and load was applied to theinorganic oxide particles by a metal spatula to measure load when theparticles were disintegrated. The measurement was carried out 50 timesand the average value of 40 measurement data excluding five largestvalues and five smallest values was taken as a crush strength value.

As this crush strength value becomes smaller, the particles are moreeasily disintegrated.

(4) Measurement of Hydrophobicity

0.2 g of the inorganic oxide particles obtained in each example wasadded to 50 mL of water in a beaker having a capacity of 250 mL andstirred by means of a magnetic stirrer. Methanol was added to theresulting dispersion by using a burette so as to carry out titrationwith a point of time when the whole amount of the sample powders got wetand suspended in the solvent in the beaker as an end point. At thispoint, methanol was guided into the liquid through a tube so that it didnot come into direct contact with the sample particles.

The volume percentage (%) of methanol in the methanol-water mixedsolvent at the end point was taken as hydrophobicity.

(5) Measurement of Agglomeration Degree

A sieve having an opening of 355 μm, a sieve having an opening of 250 μmand a sieve having an opening of 150 μm were set in upper, middle andbottom stages of the PT-R Powder Tester (trade name) of Hosokawa MicronCorporation at intervals of 2 cm. After 5 g of the inorganic oxideparticles was put on the sieve in the upper stage and vibratedvertically at an amplitude of 1 mm and a frequency of 60 Hz for 15seconds, the agglomeration degree (%) was calculated from the amounts ofthe inorganic oxide particles remaining on the sieves based on thefollowing equation. As the agglomeration degree becomes lower, theflowability of the inorganic oxide particles becomes higher.

Agglomeration degree (%)={(amount of remaining particles on topsieve+amount of remaining particles on middle sieve×0.6+amount ofremaining particles on bottom sieve×0.2)÷5 (g)}×100

(6) Measurement of Nitrogen Content

After 50 mg of silica particles was weighed and collected on a boat byusing the NC-22F high-sensitivity N.C. analyzer of Sumika ChemicalAnalysis Service, Ltd. and completely oxidized at 830° C., thequantitative analysis of a nitrogen component was carried out by TCD gaschromatography so as to measure the nitrogen content (mass %) of theinorganic oxide particles.

(7) Measurement of Amount of Metal Element Component

About 2 g of the inorganic oxide particles obtained in each example,comparative example or reference example was weighed precisely andtransferred to a platinum dish, and 10 mL of concentrated nitric acidand 10 mL of fluoric acid were added to this in this order. Theresulting dispersion was put on a hot plate set to 200° C. to be heatedso as to dry up the content. After the dried product was cooled to roomtemperature, 2 mL of concentrated nitric acid was further added, and theresulting product was put on a hot plate set to 200° C. to be heated anddissolved. After the obtained solution was cooled to room temperature,the solution which was the content of the platinum dish was transferredto a measuring flask having a capacity of 50 mL and diluted with superpure water up to a gauge line.

This sample was used to measure the amount of the metal elementcomponent by means of an ICP emission spectrometer (ICPS-1000V ofShimadzu Corporation).

(8) Measurement of Coverage of Resin Surface

0.8 g of the inorganic oxide particles obtained in each example,comparative example or reference example and 20 g of styrene-acrylicresin particles having a medium diameter of 6.1 μm were placed into a100 mL polyethylene bottle and mixed together by means of a shakingapparatus for 60 minutes. 50 different view fields of the obtained mixedparticles were observed through an field-emission-type scanning electronmicroscope (S-5500 of Hitachi High-Technologies Corporation) at amagnification of 10,000×. The obtained images were used to calculate theaverage value of the coverage of the resin surfaces from the followingequation by using an image analyzing system (IP-1000PC of Asahi KaseiCorporation). As the surface coverage becomes higher, the inorganicoxide particles are better as an external additive for toners. When thisvalue is 5% or more, it can be evaluated as a practical level.

Surface coverage (%)=area of part covered with inorganic oxideparticles/area of styrene-acrylic resin particle×100

(9) Measurement of Triboelectric Charge Quantity

Seven 50 mL screw tubular bottles were prepared, and 1 g of the mixedparticles of the inorganic oxide particles and the styrene-acrylic resinused for the measurement of the coverage of the above resin surface and99 g of a ferrite carrier having a particle diameter of 45 to 75 μm wereplaced into these bottles and left to stand at 25° C. and 50% RH for 24hours or more to control their humidities. Each of the screw tubularbottles filled with the sample after humidity control was set in theVMR-5 mix rotor of As One Corporation at a rotor revolution of 90 rpm tomix them together for 1 minute, 3 minutes, 5 minutes, 10 minutes, 30minutes, 60 minutes or 120 minutes.

The frictional charge quantity of each of the above samples was measuredby means of the TB-203 powder charge quantity measurement instrument ofKyocera Chemical Corporation after nitrogen was blown into the sample ata blow pressure of 10 kPa and a pull pressure of −5 kPa.

The frictional charge quantity of the sample after 3 minutes of mixingwas used as an index of the rate of charge rise. As this value becomeslarger, toner characteristic properties become better.

The maximum value of the frictional charge quantity is taken assaturation frictional charge quantity, and charge stability wascalculated from the following equation. As this charge stability becomeshigher, toner characteristic properties become better.

Charge stability (%)=frictional charge quantity after 120 minutes ofmixing (μC/g)/saturation frictional charge quantity (μC/g)×100

Production of Inorganic Oxide Particles which are not Surface TreatedExample 1-1

A dispersion of inorganic oxide particles was first prepared by thereaction of the sol-gel method. 150 g of 15 mass % ammonia water (1.2mass % of ammonia based on the mass of a metal alkoxide which will bedescribed hereinafter) as a basic catalyst and 1,040 g of methanol (27mass % based on the mass of the obtained dispersion) as an organicsolvent were placed into a 10-L four-necked flask and stirred at 35° C.

1,940 g of tetramethoxysilane as a metal alkoxide and 700 g of 5 mass %ammonia water (1.8 mass % of ammonia based on the mass of the metalalkoxide, a total of 3.0 mass % including ammonia contained in theammonia water placed previously) as a basic catalyst were eachindependently added directly into the resulting dispersion a little at atime. The addition speed was controlled to ensure that the additionended in 5 hours. During the sol-gel reaction, the temperature was keptat 35° C. The mass of the dispersion obtained by the above recipe was3,830 g and the concentration of silica in the dispersion was 20 mass %(766 g of silica).

10 minutes after the start of addition, the reaction liquid was clouded,thereby confirming the proceeding of the reaction. After the end ofaddition, ageing was carried out for 0.5 hour.

20 g of solid carbon dioxide (dry ice) (2.6 mass % based on silicacontained in the dispersion) was added as a coagulant to the obtaineddispersion and left to stand for 20 hours. After 20 hours, silicaparticles settled out.

The dispersion after the sedimentation of the above silica particles wasfiltered under reduced pressure by using a quantitative filter paper(hold particle diameter of 7 μm) to obtain 1,303 g of a cake(concentrate) having a silica concentration of 57 mass %. At this point,the filtrate was transparent and a filtration leak was not confirmed.The above cake was vacuum dried at 100° C. for 16 hours to obtain 804 gof silica particles. When infrared spectroscopic (IR) analysis was madeon the silica particles, no peak based on carbonic acid was detected,whereby it was confirmed that no ammonium carbonate remained.

Subsequently, the silica particles were calcined at 900° C. in air for10 hours. 743 g of silica particles which seemed to be not sintered wereobtained.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 1-1.

Example 1-2

The operation of Example 1-1 was repeated except that 20 g of ammoniumhydrogen carbonate (2.6 mass % based on silica contained in thedispersion) in a solid state was used as a coagulant in place of the dryice. Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 1-1.

Example 1-3

The operation of Example 1-1 was repeated except that the amount of thedry ice as a coagulant was changed to 200 g (26 mass % based on silicacontained in the dispersion). Various measurements were made on thedispersion and the silica particles in this example in accordance withthe above methods. The measurement results are shown in Table 1-1.

Example 1-4

The operation of Example 1-1 was repeated except that the ageing timeafter the addition of the dry ice was changed to 2 hours. Variousmeasurements were made on the dispersion and the silica particles inthis example in accordance with the above methods. The measurementresults are shown in Table 1-1

Example 1-5

The operation of Example 1-1 was repeated except that the reactiontemperature of the sol-gel reaction was changed to 15° C. Variousmeasurements were made on the dispersion and the silica particles inthis example in accordance with the above methods. The measurementresults are shown in Table 1-1.

Example 1-6

A dispersion of inorganic oxide particles was first prepared by thereaction of the sol-gel method. 210 g of 25 mass % ammonia water (3.1mass % of ammonia based on the mass of a metal alkoxide which will bedescribed hereinafter) as a basic catalyst and 310 g of methanol and 710g of isopropanol (26.8 mass % based on the mass of the obtaineddispersion) as organic solvents were placed into a 10-L four-neckedflask and stirred at 40° C.

10 minutes after 26 g of tetramethoxysilane as a metal alkoxide wasadded dropwise to the resulting dispersion, the reaction liquid wasclouded, thereby confirming the proceeding of the reaction.Subsequently, a solution consisting of 1,650 g of tetramethoxysilane asa metal alkoxide and 170 g of methanol as an organic solvent (4.5 mass %based on the mass of the obtained dispersion, a total of 31 mass %including the organic solvents placed previously) and 730 g of 25 mass %ammonia water (10.9 mass % of ammonia based on the mass of the metalalkoxide, a total of 14 mass % including ammonia contained in theammonia water placed previously) as a basic catalyst were eachindependently added directly into the resulting liquid a little at atime. The addition speed was controlled to ensure that the additionended in 2 hours. During the sol-gel reaction, the temperature was keptat 40° C. The mass of the dispersion obtained by the above recipe was3,806 g.

20 g of solid carbon dioxide (dry ice) (3.0 mass % based on silicacontained in the dispersion) was added as a coagulant to the obtaineddispersion and left to stand for 20 hours. After 20 hours, silicaparticles settled out.

The dispersion after the sedimentation of the above silica particles wasfiltered under reduced pressure by using a quantitative filter paperhaving a hold particle diameter of 7 μm to obtain 1,448 g of a cake(concentrate) having a silica concentration of 52 mass %. At this point,the filtrate was transparent and a filtration leak was not confirmed.The above cake was vacuum dried at 100° C. for 16 hours to obtain 807 gof silica particles. Subsequently, the silica particles were calcined at900° C. in air for 10 hours to obtain 753 g of silica particles whichseemed to be not sintered.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 1-1.

Example 1-7

The operation of Example 1-6 was repeated except that pressurefiltration was carried out at a pressure of 0.1 MPa by using a filterpaper having an opening size of 6 μm in place of filtration underreduced pressure using a quantitative filter paper having a holdparticle diameter of 7 μm. Various measurements were made on thedispersion and the silica particles in this example in accordance withthe above methods. The measurement results are shown in Table 1-1.

Example 1-8

The operation of Example 1-6 was repeated except that centrifugalfiltration was carried out at a revolution of 1,000 rpm by using alaminate consisting of a filter cloth having a draft quantity of 0.2cc/(cm²·sec) and a filter paper having an opening size of 6 μm in placeof filtration under reduced pressure using a quantitative filter paperhaving a hold particle diameter of 7 μm. Various measurements were madeon the dispersion and the silica particles in this example in accordancewith the above methods. The measurement results are shown in Table 1-1.

Example 1-9

A dispersion of inorganic oxide particles was first prepared by thereaction of the sol-gel method. 475 g of tetramethoxysilane as a metalalkoxide was placed into a 3-L four-necked flask, and 238 g of methanol(11 mass % based on the mass of the obtained dispersion) as an organicsolvent and 56 g of 0.035 mass % hydrochloric acid (0.003 mass % ofhydrogen chloride based on the mass of the metal alkoxide) as an acidcatalyst were added to the dispersion and stirred at room temperaturefor 10 minutes to hydrolyze tetramethoxysilane. Subsequently, a solutionprepared by dissolving 250 g of titanium tetraisopropoxide as a metalalkoxide in 500 g of isopropanol (23 mass % based on the mass of theobtained dispersion) was added to obtain a transparent compositealkoxide solution.

256 g of isopropanol (12 mass % based on the mass of the obtaineddispersion, a total of 46 mass % including methanol and isopropanolcontained in the above composite alkoxide solution) and 64 g of 25 mass% ammonia water (2.2 mass % of ammonia based on the mass of the metalalkoxide) were placed into a 5-L four-necked flask and stirred while thetemperature was kept at 40° C. The above alkoxide solution and 344 g of25 mass % ammonia water (3.9 mass % of ammonia based on the mass of themetal alkoxide, a total of 6 mass % including the above) were eachindependently added directly into the resulting liquid a little at atime. The addition speed was controlled to ensure that the additionended in 5 hours. 10 minutes after the start of addition, the reactionliquid was clouded, thereby confirming the proceeding of the reaction.After the end of addition, ageing was carried out for 0.5 hour. The massof the dispersion obtained by the above recipe was 2,183 g.

Then, 150 g of solid carbon dioxide (dry ice) (58 mass % based on thecomposite oxide particles contained in the dispersion) as a coagulantwas added to the obtained dispersion and left to stand for 4 hours.After 4 hours, silica-titania composite oxide particles settled out.

The dispersion after the sedimentation of the above particles wasfiltered under reduced pressure by using a quantitative filter paper(hold particle diameter of 5 μm) to obtain 398 g of a cake (concentrate)having a silica-titania composite oxide concentration of 62 mass %. Atthis point, the filtrate was transparent and a filtration leak was notconfirmed. The above cake was vacuum dried at 100° C. for 16 hours toobtain 260 g of silica-titania composite oxide particles. Further, thesilica-titania composite oxide particles were calcined at 1,050° C. inair for 12 hours to obtain 247 g of silica-titania composite oxideparticles which seemed to be not sintered.

Various measurements were made on the dispersion and the silica-titaniacomposite oxide particles in this example in accordance with the abovemethods. The measurement results are shown in Table 1-1.

Example 1-10

A dispersion of inorganic oxide particles was first prepared by thereaction of the sol-gel method. 4.0 g of 0.1 mass % hydrochloric acid(0.001 mass % of hydrogen chloride based on the mass of a metal alkoxidewhich will be described hereinafter) as an acid catalyst, 158 g oftetraethoxysilane as a metal alkoxide and 950 g of methanol (24 mass %based on the mass of the obtained dispersion) as an organic solvent wereplaced into a 3-L four-necked flask to carry out hydrolysis at roomtemperature for 2 hours under agitation. A solution prepared bydissolving 38 g of zirconium n-butoxide as a metal alkoxide in 400 g ofisopropanol (10 mass % based on the mass of the inorganic oxide particledispersion) was added to the obtained dispersion so as to prepare acomposite alkoxide solution.

1,980 g of methanol (51 mass % based on the mass of the obtaineddispersion) and 125 g of 25 mass % ammonia water (9.5 mass % based onthe mass of the metal alkoxide) were added to a 10-L four-necked flask.When a solution prepared by dissolving 4.0 g of tetraethoxysilane as ametal alkoxide in 80 g of methanol (2 mass % based on the mass of theobtained dispersion) was added to this liquid over 5 minutes while thissolution was maintained at 20° C., it was confirmed that the reactionliquid was slightly clouded.

The above composite alkoxide solution was added dropwise to thisreaction liquid over 2 hours. Further, a solution prepared by dissolving128 g of tetraethoxysilane as a metal alkoxide in 400 g of methanol (1mass % based on the mass of the obtained dispersion, a total of 88 mass% of the organic solvents) was added dropwise over 2 hours, and ageingwas carried out for 0.5 hour after the end of addition. The mass of thedispersion obtained by the above injection was 4,267 g.

20 g of solid carbon dioxide (dry ice) (21 mass % based on the compositeoxide particles contained in the dispersion) as a coagulant was added tothe obtained dispersion and left to stand for 20 hours. After 20 hours,silica-zirconia composite oxide particles settled out.

The dispersion after the sedimentation of the above particles wasfiltered under reduced pressure by using a quantitative filter paper(hold particle diameter of 5 μm) to obtain 153 g of a cake (concentrate)having a silica-zirconia composite oxide concentration of 58 mass %.This cake was vacuum dried at 100° C. for 16 hours to obtain 98 g ofsilica-zirconia composite oxide. Further, the silica-zirconia compositeoxide was calcined at 1,000° C. in air for 6 hours to obtain 89 g ofsilica-zirconia composite oxide particles which seemed to be notsintered.

Various measurements were made on the dispersion and the silica-zirconiacomposite oxide particles in this example in accordance with the abovemethods. The measurement results are shown in Table 1-1.

Example 1-11

The operation of Example 1-1 was repeated except that a mixed solventconsisting of 780 g of methanol and 260 g of isopropyl alcohol was usedas an organic solvent in the reaction of the sol-gel method in place of1,040 g of methanol. Various measurements were made on the dispersionand the silica particles in this example in accordance with the abovemethods The measurement results are shown in Table 1-1.

Example 1-12

The operation of Example 1 was repeated except that 20 g of ammoniumcarbonate (2.6 mass % based on inorganic oxide particles contained inthe dispersion) was used in place of the dry ice. Various measurementswere made on the dispersion and the silica particles in this example inaccordance with the above methods. The measurement results are shown inTable 1-1.

Example 1-13

The operation of Example 1 was repeated except that 20 g of ammoniumcarbamate (2.6 mass % based on inorganic oxide particles contained inthe dispersion) was used in place of the dry ice. Various measurementswere made on the dispersion and the silica particles in this example inaccordance with the above methods. The measurement results are shown inTable 1-1.

Example 1-14

The operation of Example 1 was repeated except that the dryingtemperature was set to 150° C. When the nitrogen content was measured,it was 0.01%.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 1-1.

Exmaple 1-15

The operation of Example 2 was repeated except that the dryingtemperature was set to 150° C. When the nitrogen content was measured,it was 0.01%.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 1-1.

Comparative Example 1-1

When filtration was carried out without adding dry ice and withoutcarrying out the subsequent stirring operation in Example 1-1, thedispersion passed through a filter paper and silica could not becollected. Therefore, after the obtained dispersion was concentratedunder reduced pressure to remove the organic solvent to a certainextent, the dispersion was vacuum dried at 100° C. for 16 hours and thencalcined at 900° C. in air for 10 hours to obtain silica particles.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 1-1.

Reference Example 1-1

A dispersion of silica particles was obtained by mixing 10 g of thedried and calcined silica particles obtained in the above Example 1-1with 90 g of pure water and stirring the mixture for 1 hour. When thisdispersion was filtered under reduced pressure by using a quantitativefilter paper (hold particle diameter of 7 μm), the dispersion passedthrough a filter paper and silica particles could not be collected.

Then, after the above dispersion was vacuum dried at room temperatureand the dispersion medium was distilled off to a certain extent, thedispersion was vacuum dried at 100° C. for 16 hours and then calcined at900° C. in air for 10 hours to obtain silica particles. Variousmeasurements were made on the silica particles in accordance with theabove methods. The measurement results are shown in Table 1-1.

Reference Example 1-2

A dispersion of silica particles was obtained by mixing 10 g of thedried and calcined silica particles obtained in the above Example 1-1with 90 g of a 5 mass % aqueous solution of ammonium carbonate andstirring the mixture for 1 hour. When this dispersion was filtered underreduced pressure by using a quantitative filter paper (hold particlediameter of 7 μm), a silica cake was collected. At this point, thefiltrate was transparent.

The above silica cake was vacuum dried at 100° C. for 16 hours and thencalcined at 900° C. in air for 10 hours to collect 10 g of silicaparticles.

It is understood from the results shown in Table 1-1 below that theinorganic oxide particles obtained by the production method of thepresent invention have extremely low crush strength and the formation ofa firm agglomerate requiring a disintegration treatment is prevented inthe step of concentrating a dispersion of the inorganic oxide particlesand the drying step after concentration.

TABLE 1-1 Concentrate Content of Dispersion Concentration After dryingAfter calcination metal Median of inorganic Median Variation MedianVariation Crush element diameter oxide diameter coefficient diametercoefficient strength (ppm) (μm) (mass %) (μm) (%) (μm) (%) (N) Na Al FeEx. 0.090 57 0.088 20 0.082 21 0.21 0.7 0.1 0.1 1-1 Ex. 0.090 55 0.08919 0.083 20 0.19 0.7 0.1 0.1 1-2 Ex. 0.089 56 0.087 19 0.082 21 0.19 0.80.2 0.1 1-3 Ex. 0.089 59 0.089 18 0.083 19 0.22 0.7 0.1 0.1 1-4 Ex. 0.4058 0.42 16 0.38 16 0.21 0.9 0.2 0.2 1-5 Ex. 0.82 52 0.83 14 0.78 15 0.190.9 0.2 0.1 1-6 Ex. 0.82 51 0.84 15 0.78 15 0.19 0.9 0.2 0.1 1-7 Ex.0.83 65 0.83 14 0.78 15 0.19 0.9 0.2 0.2 1-8 Ex. 0.61 62 0.61 10 0.58 110.21 1.0 0.2 0.2 1-9 Ex. 0.14 58 0.13 6 0.14 7 0.23 1.0 0.2 0.2 1-10 Ex.0.40 59 0.41 15 0.38 16 0.21 0.8 0.1 0.1 1-11 Ex. 0.090 54 0.089 190.082 21 0.20 0.7 0.1 0.1 1-12 Ex. 0.090 55 0.089 18 0.082 20 0.19 0.80.1 0.1 1-13 Ex. 0.090 57 0.088 20 0.082 21 0.20 0.7 0.1 0.1 1-14 Ex.0.090 55 0.089 19 0.083 20 0.19 0.7 0.1 0.1 1-15 C.Ex. 0.089 — 0.095 424.5 95 1.3 1.1 0.2 0.1 1-1 R.Ex. 0.090 — 0.096 41 4.4 96 1.4 1.1 0.2 0.11-1 Ex.: Example C.Ex.: Comparative Example R.Ex.: Reference Example

Production of Surface Treated Inorganic Oxide Particles Example 1-16

400 g of silica particles which had been dried at 100° C. for 6 hoursand obtained in the same manner as in the above Example 1-1 was placedinto the vessel of a 20-L mixer and heated at 250° C. at the same timeas the substitution of the inside of the vessel by nitrogen. After thecirculation of nitrogen was continued at a rate of 10 L/min for 15minutes, the vessel was sealed up, and steam was introduced at an insidepartial pressure of the vessel of 60 kPa. 120 g of hexamethyldisilazane(30 parts by mass based on 100 parts by mass of the silica particles)was sprayed upon the silica particles from a one-fluid nozzle while thecontent of the vessel was stirred, and agitation was continued for 60minutes to carryout a surface treatment. After the vessel of the mixerwas opened to substitute the atmosphere by a nitrogen gas, the surfacetreated silica particles were taken out.

The hydrophobicity and crush strength values of the silica particlesbefore and after the surface treatment in this example were evaluated bythe above methods. The evaluation results are shown in Table 1-2.

Example 1-17

The operation of the above Example 1-16 was repeated except that 400 gof silica particles which had been dried at 100° C. for 6 hours andobtained in the same manner as in the above Example 1-11 was used. Theevaluation results are shown in Table 1-2.

Example 1-18

140 g of silica particles which had been dried at 100° C. for 6 hoursand obtained in the same manner as in the above Example 1-11 and 700 gof toluene were placed into a 1-L four-necked flask and stirred at roomtemperature. 1.68 g of amino modified oil (1.2 parts by mass based on100 parts by mass of the silica particles) (X-22-161A of Shin-EtsuChemical Co., Ltd.) was added into the flask and heated at 110° C. underreflux for 1 hour. Thereafter, the solvent was distilled off underreduced pressure to obtain surface treated silica particles.

The hydrophobicity and crush strength values of the silica particlesbefore and after the surface treatment in this example were evaluated bythe above methods. The evaluation results are shown in Table 1-2.

Example 1-19

140 g of silica particles which had been dried at 100° C. for 6 hoursand obtained in the same manner as in the above Example 1-11 and 700 gof toluene were placed into a 1-L four-necked flask and stirred at roomtemperature. 3.76 g of decyltrimethoxysilane (2.7 parts by mass based on100 parts by mass of the silica particles) was added into the flask andheated at 110° C. under reflux for 1 hour. Thereafter, the solvent wasdistilled off under reduced pressure to obtain surface treated silicaparticles.

The hydrophobicity and crush strength values of the silica particlesbefore and after the surface treatment in this example were evaluated bythe above methods. The evaluation results are shown in Table 1-2.

TABLE 1-2 Hydrophobicity (vol %) Crush strength (N) Before After BeforeAfter surface surface surface surface treatment treatment treatmenttreatment Ex. 1-16 0 62 0.21 0.02 Ex. 1-17 0 65 0.21 0.02 Ex. 1-18 0 590.21 0.02 Ex. 1-19 0 50 0.21 0.02

Production of Surface Treated Inorganic Oxide Particles Example 2-1

150 g of 15 mass % ammonia water (1.2 mass % of ammonia based on themass of a metal alkoxide which will be described hereinafter) as a basiccatalyst and 1,040 g of methanol (27 mass % based on the mass of theobtained inorganic oxide particle dispersion) as an organic solvent wereplaced into a 10-L four-necked flask and stirred at 35° C.

1,940 g of tetramethoxysilane as a metal alkoxide and 700 g of 5 mass %ammonia water (1.8 mass % of ammonia based on the mass of the metalalkoxide, a total of 3.0 mass % including ammonia contained in theammonia water placed previously) as a basic catalyst were eachindependently added directly into the obtained liquid a little at atime. The addition speed was controlled to ensure that the additionended in 5 hours. The mass of the inorganic oxide particle dispersionobtained by the above recipe was 3,830 g, and the concentration ofsilica in the dispersion was 20 mass % (766 g of silica).

10 minutes after the start of addition, the reaction liquid was clouded,thereby confirming the proceeding of the reaction.

After the end of addition, ageing was carried out for 0.5 hour and then230 g of hexamethyldisilazane (30 mass % based on silica contained inthe dispersion) as a surface treating agent was added. After addition,stirring was carried out at 35° C. for 1 hour to make a surfacetreatment on the inorganic oxide particle dispersion.

1,530 g of a 10 mass % ammonium hydrogen carbonate aqueous solution (153g of ammonium hydrogen carbonate, 20 mass % based on silica contained inthe dispersion) was added to the obtained dispersion containing thesurface treated inorganic oxide particles. After the addition of theammonium hydrogen carbonate aqueous solution, stirring was continued foranother 2 hours.

The obtained dispersion after the addition of the ammonium hydrogencarbonate aqueous solution was filtered under reduced pressure tocollect a cake. At this point, a filtration leak was not confirmed.

The cake collected by the above filtration was dried under reducedpressure at 100° C. for 24 hours to obtain 790 g of surface treatedsilica particles.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 2-1.

Example 2-2

The operation of Example 2-1 was repeated except that the stirring timeafter the addition of a 10 mass % ammonium hydrocarbon carbonate aqueoussolution was changed to 24 hours. The measurement results are shown inTable 2-1.

Example 2-3

The operation of Example 2-1 was repeated except that the stirringtemperature after the addition of hexamethyldisilazane was changed to60° C. The measurement results are shown in Table 2-1.

Example 2-4

The operation of Example 2-1 was repeated except that drying was carriedout at 25° C. under atmospheric pressure for 24 hours and then at 25° C.under reduced pressure for 24 hours after filtration. The measurementresults are shown in Table 2-1.

Example 2-5

The operation of Example 2-1 was repeated except that 780 g of methanoland 260 g of isopropyl alcohol were used as organic solvents. Themeasurement results are shown in Table 2-1.

Example 2-6

210 g of 25 mass % ammonia water (3.1 mass % of ammonia based on themass of a metal alkoxide) as a basic catalyst and 310 g of methanol and710 g of isopropyl alcohol (26.8 mass % based on the mass of theobtained inorganic oxide particle dispersion) as organic solvents wereplaced into a 5-L four-necked flask and stirred at 40° C. 26 g oftetraethoxysilane as a metal alkoxide was added dropwise to the obtainedliquid. 10 minutes after addition, the reaction liquid was clouded,thereby confirming the proceeding of the reaction.

A solution consisting of 1,650 g of tetramethoxysilane as a metalalkoxide and 170 g of methanol (4.5 mass % based on the mass of theinorganic oxide particle dispersion, a total of 31 mass % of thealcohols) as an organic solvent and 730 g of 25% ammonia water (10.9mass % of ammonia based on the mass of the metal alkoxide, a total of 14mass % including ammonia contained in the ammonia water placedpreviously) as a basic catalyst were each independently added directlyinto the obtained dispersion a little at a time. The addition speed wascontrolled to ensure that addition ended in 2 hours.

The mass of the inorganic oxide particle dispersion obtained by theabove recipe was 3,806 g, and the concentration of silica contained inthe dispersion was 20 mass % (753 g of silica).

After the end of addition, ageing was carried out for 0.5 hour and then226 g of hexamethyldisilazane (30 mass % based on silica contained inthe dispersion) as a surface treating agent was added. After addition,stirring was carried out at 35° C. for 1 hour to make a surfacetreatment on the inorganic oxide particle dispersion.

1,510 g of a 10 mass % aqueous solution of ammonium hydrogen carbonate(151 g of ammonium hydrogen carbonate, 20 mass % based on silicacontained in the dispersion) was added to the obtained dispersioncontaining the surface treated inorganic oxide particles. After theaddition of the ammonium hydrogen carbonate aqueous solution, stirringwas continued for another 2 hours.

The above dispersion after the addition of the ammonium hydrogencarbonate aqueous solution was filtered under reduced pressure tocollect a cake. At this point, a filtration leak was not confirmed.

The cake collected by the above filtration was dried under reducedpressure at 100° C. for 24 hours to obtain 776 g of surface treatedsilica particles.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 2-1.

Example 2-7

The operation of Example 2-1 was repeated except that 77.6 g of dimethylsilicone oil (10 mass % based on silica contained in the dispersion) wasadded in place of hexamethyldisilazane. The measurement results areshown in Table 2-1.

Example 2-8

The operation of Example 2-1 was repeated except that the step of adding114.9 g of decyltrimethoxysilane (15 mass % based on silica contained inthe dispersion) as a surface treating agent and ageing for 1 hour wereadded before the addition of hexamethyldisilazane. The measurementresults are shown in Table 2-1.

Example 2-9

The operation of Example 2-6 was repeated except that centrifugalfiltration at a revolution of 1,000 rpm was carried out by using afilter cloth (draft quantity of 1.2 cc/(cm2·sec)) in place of filtrationunder reduced pressure. The measurement results are shown in Table 2-1.

Example 2-10

The operation of Example 2-1 was repeated except that the amount of theammonium hydrogen carbonate aqueous solution was changed to 1,149 g(114.9 g of ammonium hydrogen carbonate, 15 mass % based on silicacontained in the dispersion). The measurement results are shown in Table2-1.

Example 2-11

The operation of Example 2-1 was repeated except that 153 g of ammoniumhydrogen carbonate (20 mass % based on silica contained in thedispersion) was added as a solid and not as an aqueous solution and thestirring time after the addition of ammonium hydrogen carbonate waschanged to 72 hours. The measurement results are shown in Table 2-1.

Example 2-12

The operation of Example 2-1 was repeated except that 383 g of dry ice(50 mass % of CO₂ based on silica contained in the dispersion) was addedin place of the ammonium carbonate aqueous solution.

The filtration operation could be carried out without a problem exceptthat there was a slight filtration leak in the initial stage of thefiltering step of this example.

The measurement results are shown in Table 2-1.

Example 2-13

The operation of Example 2-2 was repeated except that the amount of theammonium carbonate aqueous solution was changed to 1,530 g (153 g ofammonium hydrogen carbonate, 20 mass % based on silica contained in thedispersion). The measurement results are shown in Table 2-1.

Example 2-14

The operation of Example 2-1 was repeated except that the amount of theammonium hydrogen carbonate aqueous solution was changed to 383 g (38.3g of ammonium hydrogen carbonate, 5 mass % based on silica contained inthe dispersion).

Although the silica particle contained in the dispersion passed througha filter paper in the initial stage of the filtering step and filtrationtook long, a cake was collected. The collected cake was dried at 100° C.under reduced pressure for 24 hours to obtain 75 g of surface treatedsilica particles.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 2-1.

Example 2-15

The operation of Example 2-1 was repeated except that the amount of theammonium hydrogen carbonate aqueous solution was changed to 766 g (76.6g of ammonium hydrogen carbonate, 10 mass % based on silica contained inthe dispersion).

Although the silica particle contained in the dispersion passed througha filter paper in the initial stage of the filtering step and filtrationtook long, a cake was collected. The collected cake was dried at 100° C.under reduced pressure for 24 hours to obtain 265 g of surface treatedsilica particles.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 2-1.

Example 2-16

The operation of Example 2-1 was repeated except that 153 g of ammoniumhydrogen carbonate (20 mass % based on silica contained in thedispersion) was added as a solid and not as an aqueous solution.

Although most of the silica particles contained in the dispersion passedthrough a filter paper in the filtering step of this example, a cakecould be collected.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 2-1.

Example 2-17

The operation of Example 2-1 was repeated except that 153 g of dry ice(20 mass % of CO₂ based on silica contained in the dispersion) was addedin place of the ammonium hydrogen carbonate aqueous solution.

Although most of the silica particles contained in the dispersion passedthrough a filter paper in the filtering step of this example, a cakecould be collected. The collected cake was dried at 100° C. underreduced pressure for 24 hours to obtain 68 g of surface treated silicaparticles.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 2-1.

Example 2-18

The operation of Example 2-1 was repeated except that 1,530 g of 10 mass% ammonium carbamate (153 g of ammonium carbamate, 20 mass % based onsilica contained in the dispersion) was added in place of the ammoniumhydrogen carbonate aqueous solution.

In the filtering step of this example, a filtration leak was not seen.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 2-1.

Example 2-19

The operation of Example 2-1 was repeated except that the dryingtemperature was changed to 150° C. When the nitrogen content of theobtained silica particles, it was 0.01 mass %.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 2-1.

Comparative Example 2-1

When filtration was carried out without adding an ammonium hydrogencarbonate aqueous solution and without carrying out the subsequentstirring operation in the above Example 2-1, the dispersion passedthrough a filter paper and silica could not be collected. Therefore, theobtained dispersion was concentrated under reduced pressure to obtainsilica.

Various measurements were made on the dispersion and the silicaparticles in this example in accordance with the above methods. Themeasurement results are shown in Table 2-1.

Reference Example 2-1

The operation of Example 2-1 was repeated except thathexamethyldisilazane was not added and the subsequent stirring operationwas not carried out.

The measurement results are shown in Table 2-1.

As obvious from Table 2-1, it is understood that surface treatedinorganic oxide particles having low crush strength and excellentdisintegration properties are obtained by the method in the aboveExamples 2-1 to 2-19. In the method of the present invention,particularly in Examples 2-1 to 2-10, particles can be easily collectedfrom a dispersion of surface treated inorganic oxide particles by simplefiltration at a high efficiency.

TABLE 2-1 Yield of Before surface surface treated treatment Surfacetreatment, after drying inorganic Median Median Variation Crush Contentof metal oxide diameter diameter coefficient Hydrophobicity strengthelement (ppm) particles (μm) (μm) (%) (vol %) (N) Na Al Fe (g) Ex. 2-10.090 0.090 20 51 0.02 0.9 0.2 0.1 790 Ex. 2-2 0.090 0.090 20 61 0.010.9 0.2 0.1 775 Ex. 2-3 0.090 0.090 20 55 0.02 1.0 0.1 0.1 771 Ex. 2-40.090 0.090 20 50 0.04 1.0 0.2 0.1 766 Ex. 2-5 0.40 0.40 15 50 0.02 1.00.2 0.1 765 Ex. 2-6 0.82 0.82 14 50 0.03 0.9 0.2 0.1 691 Ex. 2-7 0.0900.090 20 27 0.04 1.1 0.2 0.2 780 Ex. 2-8 0.090 0.090 20 64 0.01 1.0 0.20.2 775 Ex. 2-9 0.090 0.090 20 50 0.02 0.9 0.2 0.1 755 Ex. 2-10 0.0900.090 20 51 0.02 1.0 0.2 0.1 758 Ex. 2-11 0.090 0.090 20 59 0.02 0.9 0.20.2 778 Ex. 2-12 0.090 0.090 20 58 0.02 0.8 0.2 0.2 740 Ex. 2-13 0.0900.091 20 60 0.02 0.9 0.2 0.2 791 Ex. 2-14 0.090 0.092 23 49 0.06 0.8 0.20.1  75 Ex. 2-15 0.090 0.091 21 49 0.05 0.9 0.2 0.1 265 Ex. 2-16 0.0900.091 21 50 0.05 0.9 0.2 0.1 125 Ex. 2-17 0.090 0.091 21 50 0.05 0.8 0.20.1  68 Ex. 2-18 0.090 0.090 20 52 0.02 0.9 0.2 0.1 756 Ex. 2-19 0.0900.090 20 52 0.02 0.9 0.2 0.1 788 C.Ex. 2-1 0.090 0.095 35 48 0.18 1.10.2 0.1   770*⁾ R.Ex. 2-1 0.090 0.089 20 0 0.21 1.0 0.2 0.1 760 Ex.:Example C.Ex.: Comparative Example R.Ex.: Reference Example ^(*))Themethod of collecting silica in Comparative Example 2-1 differs from themethod in other examples.

Example 2-20

The agglomeration degree of the surface treated silica particlesobtained in the above Example 2-2 without a pretreatment(disintegration) and after the pretreatment was made under the followingconditions was measured in accordance with the above method. The resultsare shown in Table 2-2.

(Pretreating Method)

15 g of silica and 15 g of glass beads having a diameter of 5 mm (BZ-5glass bead of As One Corporation) were put into the I-Boy wide-mouthbottle having a capacity of 100 mL (trade name, manufactured by As OneCorporation), and the bottle was set in a vertical shaking apparatus(SA-31 of Yamato Scientific Co., Ltd.) to shake it at an amplitude of 5cm and a rate of 270 times/min for 30 minutes.

The disintegration conditions were very mild.

Comparative Example 2-2

Surface treated silica particles were prepared in accordance withExample 1 of JP-A 2000-44226.

2,297 g of a silica dispersion before a surface treatment obtained inthe same manner as in Example 2-1 was placed into a 5-L four-neckedflask, 1,600 g of water was added when 678 g of methanol was distilledoff by heating at 60 to 70° C., and then 195 g of methanol was distilledoff by heating at 70 to 90° C. to obtain an aqueous dispersion of silicafine particles.

115.8 g of methyl trimethoxysilane and 46.6 g of 5.4 mass % ammoniawater were added dropwise to this aqueous dispersion at room temperatureover 0.5 hour and stirring was continued for 15 hours after addition tocarry out the surface treatment of the silica fine particles.

After 1,000 g of methyl isobutyl ketone was added to the dispersioncontaining surface treated silica obtained as described above, theresulting mixture was heated at 80 to 110° C. to distill off 1,338 g ofboth methanol and water over 7 hours.

357.6 g of hexamethyldisilazane was added to the obtained dispersion atroom temperature and heated at 120° C. to carry out a reaction for 3hours so as to trimethylsilylate the surfaces of silica particles.Thereafter, the solvent was distilled off under reduced pressure toobtain 520 g of surface treated silica.

The agglomeration degree without a pretreatment and after thepretreatment was measured in the same manner as in the above Example2-20 except that the surface treated silica particles obtained abovewere used. The results are shown in Table 2-2.

Comparative Example 2-3

Surface treated silica particles were prepared in accordance withSynthesis Example 1 of JP-A 2002-108001.

600 g of a silica dispersion (120 g of silica) before a surfacetreatment obtained in the same manner as in the above Example 2-1 washeated to remove methanol, and toluene was added and heated to removewater. 48 g of hexamethyldisilazane (40 mass % based on silica containedin silica slurry) was added to the resulting mixture, heated at 120° C.for 2 hours under agitation and further heated to remove toluene. Theresulting mixture was dried at 100° C. under reduced pressure for 24hours to obtain 107 g of surface treated silica.

The agglomeration degree without a pretreatment and after thepretreatment was measured in the same manner as in the above Example2-20 except that the surface treated silica particles obtained abovewere used. The results are shown in Table 2-2.

TABLE 2-2 Agglomeration degree (%) Without pretreatment Afterpretreatment Example 2-20 44 27 Comparative 63 66 Example 2-2Comparative 69 78 Example 2-3

Production of Surface Treated Inorganic Oxide Particles Example 3-1 (1)Reaction Step

150 g of 15 mass % ammonia water (1.2 mass % based on the mass of ametal alkoxide which will be described hereinafter) as a basic catalystand 1,040 g of methanol (27 mass % based on the mass of an inorganicoxide particle dispersion produced by a reaction) as an organic solventwere placed into a 10-L four-necked flask and stirred at 35° C. 1,940 gof tetramethoxysilane as a metal alkoxide and 700 g of 5 mass % ammoniawater (1.8 mass % of ammonia based on the mass of the metal alkoxide, atotal of 3.0 mass % including the ammonia water placed previously) as abasic catalyst were each independently added directly into the resultingliquid a little at a time. The addition speed was controlled to ensurethat the addition ended in 5 hours. 10 minutes after the start ofaddition, the reaction liquid was clouded, thereby confirming theproceeding of a reaction. After the end of addition, ageing was carriedout at 35° C. for 0.5 hour to obtain a dispersion of inorganic oxideparticles.

The mass of the dispersion of inorganic oxide particles was 3,830 g, andthe concentration of silica in the dispersion was 20 mass % (766 g ofsilica).

(2) First Surface Treating Step

230 g of hexamethyldisilazane (30 mass % based on silica contained inthe dispersion) as a surface treating agent was added to the dispersionobtained in the above step (1) and stirred at 35° C. for 1 hour.

(3) Coagulant Adding Step

1,530 g of a 10 mass % ammonium hydrogen carbonate aqueous solution (153g of ammonium hydrogen carbonate, 20 mass % based on silica contained inthe dispersion) as a coagulant was added to the surface treated silicadispersion obtained in the above step (2) and then stirred at 35° C. for2 hours.

(4) Particle Collection Step

The dispersion after the addition of the coagulant obtained in the abovestep (3) was filtered under reduced pressure to obtain a cake. At thispoint, a filtration leak was not confirmed.

(5) Particle Drying Step

The cake collected in the above step (4) was dried under reducedpressure at 150° C. for 24 hours to obtain 790 g of silica particlesafter the first surface treatment.

The steps (1) to (5) are the same as in the above Example 2-1.

(6) Second Surface Treating Step

The silica particles after the first surface treatment obtained in theabove step (5) were placed into a 20-L pressure vessel and heated up to230° C. After the inside of the vessel was substituted by a nitrogenatmosphere, it was sealed up under atmospheric pressure, and 16 g ofwater was sprayed upon the particles under agitation. Thereafter,stirring was continued for 15 minutes, depressurization was carried out,and 95 g of hexamethyldisilazane was sprayed upon the particles. Afterstirring was further continued for another 1 hour, 400 g of silicaparticles after a second surface treatment were obtained bydepressurization.

Various measurements were made on the obtained silica particles inaccordance with the above methods. The measurement results are shown inTable 3-1.

Example 3-2

Silica particles after the second surface treatment were obtained in thesame manner as in Example 3-1 except that the second surface treatingstep (6) was changed to the following step (6′) in the above Example3-1. Various measurements were made on the obtained silica particles inaccordance with the above methods. The measurement results are shown inTable 3-1.

(6′) Second Surface Treating Step Alternative Method 1

The silica particles after the first surface treatment obtained in thestep (5) were placed into a 20-L pressure vessel and heated up to 230°C. After the inside of the vessel was substituted by a nitrogenatmosphere, it was sealed up under atmospheric pressure, and 50 g ofmethyltrimethoxysilane was sprayed upon the particles under agitation.After stirring was continued for 1 hour, depressurization was carriedout, 16 g of water was sprayed upon the particles, and stirring wascontinued for 15 minutes. After depressurization, 95 g ofhexamethyldisilazane was sprayed upon the particles, and stirring wasfurther continued for another 1 hour. Then, 240 g of silica particlesafter the second surface treatment were obtained by depressurization.

Example 3-3

Silica particles after the second surface treatment were obtained in thesame manner as in Example 3-1 except that the second surface treatingstep (6) was changed to the following step (6″) in the above Example3-1. Various measurements were made on the obtained silica particles inaccordance with the above methods. The measurement results are shown inTable 3-1.

(6″) Second Surface Treating Step Alternative Method 2

The silica particle after the first surface treatment obtained in theabove step (5) were placed into a 20-L pressure vessel and heated up to230° C. After the inside of the vessel was substituted by a nitrogenatmosphere, it was sealed up under atmospheric pressure, and 16 g ofwater was sprayed upon the particles under agitation. Thereafter,stirring was continued for 15 minutes, depressurization was carried out,and 95 g of hexamethyldisilazane was sprayed upon the particles. Afterstirring was continued for 1 hour, depressurization was carried out, 3 gof silicone oil having a viscosity of 50 cps was further sprayed uponthe particles, and stirring was further continued for another 1 hour.Then, 300 g of silica particles after the second surface treatment wasobtained by depressurization.

Comparative Example 3-1

Attempts were made to carry out the particle collection step (4) withoutcarrying out the coagulant addition step (3) in the above Example 3-1but the particles passed through the a filter paper and could not becollected. Then, the solvent contained in the dispersion was removedunder reduced pressure to collect silica. Thereafter, the operation ofthe second surface treating step (6) in Example 3-1 was repeated toobtain 600 g of surface treated silica particles. Various measurementswere made on the obtained silica particles in accordance with the abovemethods. The measurement results are shown in Table 3-1.

Table 3-1 below shows the evaluation results of the particles obtainedin the above Examples 3-1 to 3-3 and Comparative Example 3-1 as well asthe evaluation results of the particles obtained in the aboveComparative Examples 2-2 and 2-3 and the evaluation results of theparticles obtained in the above Example 2-1 as Reference Example 3-1.

The coverages of the resin surface of the particles obtained inComparative Examples 3-1, 2-2 and 2-3 were less than 5% which means thatthe particles rarely adhered to the surface of the resin. Therefore, asit was judged that the particles did not reach a practical level, thetriboelectric charge quantity was not measured.

TABLE 3-1 Triboelectric charge quantity Content of Saturation metal Rateof triboelectric Hydro- Amount element Surface charge charge Chargephobicity Agglomeration of N (ppm) coverage rise quantity stability (vol%) degree (%) (mass %) Na Al Fe (%) (μc/g) (μc/g) (%) Ex. 3-1 70 42 0.010.9 0.2 0.1 17 28 43 63 Ex. 3-2 68 41 0.01 0.9 0.2 0.1 12 32 37 70 Ex.3-3 67 48 0.01 1.0 0.1 0.1 11 26 48 81 Ex. 3-1 63 66 0.09 0.9 0.2 0.1Less than 5 — — — C. 64 66 0.09 1.1 0.2 0.2 Less than 5 — — — Ex. 2-2 C.53 78 0.12 1.0 0.2 0.1 Less than 5 — — — Ex. 2-3 R. 61 46 0.01 0.9 0.20.1  9 17 26 34 Ex. 3-1 (Ex. 2-1) Ex.: Example C.Ex.: ComparativeExample R.Ex.: Reference Example

EFFECT OF THE INVENTION

According to the present invention, there is provided a method foreasily producing inorganic oxide particles which do not agglomeratefirmly and are excellent in flowability.

The inorganic oxide particles produced by the method of the presentinvention have weak agglomeration force and excellent disintegrationproperties. Further, although the coagulant used in the method of thepresent invention can be existent stably in a synthetic solution as itis or in the state of a derivative thereof, it is decomposed into carbondioxide, ammonia and water by heating at about 35 to 60° C. Therefore,it can be easily decomposed and removed by heating at the time ofdrying. Consequently, according to the method of the present invention,there is no possibility that impurities derived from the coagulantremain in the product, thereby making it possible to obtain inorganicoxide particles having high purity. This is a great advantage ascompared with a conventional method using a metal salt which readilyremains in particles.

The inorganic oxide particles produced by the method of the presentinvention can be advantageously used as a filler for resins and rubbersor an abrasive.

When the inorganic oxide particles produced by the method of the presentinvention are surface treated inorganic oxide particles whose surfaceshave been hydrophobized, the particles are hydrophobic as well as havingexcellent disintegration properties and a narrow particle sizedistribution. Therefore, they are useful as an external additive forelectrophotographic toners.

1-9. (canceled)
 10. A method for producing inorganic oxide particles,comprising at least the following steps of: coagulating a dispersionobtained by carrying out the hydrolysis reaction and thepolycondensation reaction of a metal alkoxide in the presence of a basiccatalyst by using of a mixture of water and an alcohol as a solvent;filtering the dispersion to obtain particles; and drying the particles,wherein the step of coagulating the dispersion is carried out by addinga coagulant comprising at least one compound selected from the groupconsisting of carbon dioxide, ammonium carbonate, ammonium hydrogencarbonate and ammonium carbamate to the dispersion.
 11. The method forproducing inorganic oxide particles according to claim 10, wherein thestep of coagulating the dispersion is carried out after the step ofadding at least one surface treating agent selected from the groupconsisting of a silicone oil, a silane coupling agent and a silazane tothe dispersion; and the inorganic oxide particles to be produced aresurface treated inorganic oxide particles.
 12. The method for producinginorganic oxide particles according to claim 11, wherein the surfacetreatment of the inorganic oxide particles is carried out by furtheradding at least one surface treating agent selected from the groupconsisting of a silicone oil, a silane coupling agent and a silazane tothe dried inorganic oxide particles after the drying step.
 13. Themethod for producing inorganic oxide particles according to claim 10,wherein the surface treatment of the inorganic oxide particles iscarried out by adding at least one surface treating agent selected fromthe group consisting of a silicone oil, a silane coupling agent and asilazane to the dried oxide particles after the drying step; and theinorganic oxide particles to be produced are surface treated inorganicoxide particles.
 14. The method for producing inorganic oxide particlesaccording to claim 10, wherein the amount of the coagulant is 0.001 partor more by mass based on 100 parts by mass of the inorganic oxideparticles to be produced.
 15. The method for producing inorganic oxideparticles according to claim 11, wherein the amount of the coagulant is15 parts or more by mass based on 100 parts by mass of the inorganicoxide particles to be produced.
 16. Inorganic oxide particles producedby the method of claim
 10. 17. Surface treated inorganic oxide particlesproduced by the method of claim
 11. 18. The surface treated inorganicoxide particles according to claim 17, wherein, after a sieve having anopening of 355 μm, a sieve having an opening of 250 μm and a sievehaving an opening of 150 μm (all the sieves have a diameter of 75 mmbased on JIS Z8801) are placed one upon another at intervals of 2 cm inthis order from the top, 5 g of the particles is put on the top sieveand vibrated vertically at an amplitude of 1 mm and a frequency of 60 Hzfor 15 seconds, the agglomeration degree calculated from the amounts ofparticles remaining on these sieves based on the following equation is60% or less.Agglomeration degree (%)={(amount of remaining particles on topsieve+amount of remaining particles on middle sieve×0.6+amount ofremaining particles on bottom sieve×0.2)}÷initial mass of surfacetreated inorganic oxide particles×100.
 19. The method for producinginorganic oxide particles according to claim 11, wherein the amount ofthe coagulant is 0.001 part or more by mass based on 100 parts by massof the inorganic oxide particles to be produced.
 20. The method forproducing inorganic oxide particles according to claim 12, wherein theamount of the coagulant is 0.001 part or more by mass based on 100 partsby mass of the inorganic oxide particles to be produced.
 21. The methodfor producing inorganic oxide particles according to claim 13, whereinthe amount of the coagulant is 0.001 part or more by mass based on 100parts by mass of the inorganic oxide particles to be produced.
 22. Themethod for producing inorganic oxide particles according to claim 12,wherein the amount of the coagulant is 15 parts or more by mass based on100 parts by mass of the inorganic oxide particles to be produced. 23.The method for producing inorganic oxide particles according to claim13, wherein the amount of the coagulant is 15 parts or more by massbased on 100 parts by mass of the inorganic oxide particles to beproduced.
 24. Inorganic oxide particles produced by the method of claim11.
 25. Inorganic oxide particles produced by the method of claim 12.26. Inorganic oxide particles produced by the method of claim
 13. 27.Surface treated inorganic oxide particles produced by the method ofclaim
 12. 28. Surface treated inorganic oxide particles produced by themethod of claim 13.